Saturday, 23 June 2007

'Navigation Using the Sun' Guest Article by Mark Bradshaw

'Where am I ?'

A basic introduction to a few methods of ROUGH direction finding using the position and movement of the sun in the sky.

The sun rises in the east and it sets in the west. In the northern hemisphere at 1200 local time it is due south, at 0600 it is due east and at 1800 it is due west. Its travel across the skies is constant, it neither speeds up or slows down - so with those irrefutable facts determined we can work out the position of the sun in the sky using only the time of day.
We are going to look at three methods of finding the suns position; each method takes longer, and is more accurate, than the last.

Instant Method
• Ensure your (analogue) watch is set to local or solar time.
• Keeping the watch face horizontal point the hour hand as accurately as possible at the sun.
• An imaginary line that exactly bisects the angle between the hour hand and the 12 O’clock
position on the watch points due SOUTH.
• Continue that line in the opposite direction and you have north.
• Mark north with a stick or stone before you move around and lose its position.

The higher the sun is in the sky the more difficult it can be to determine its
Practice this skill when you have a compass handy so you become proficient without having to think too much about what you are doing, and practice without using a watch but visualising a clock face.
Even when you have a map and compass available you can use this method to make sure you don’t make one of those very common and embarrassing ‘180 degree’ errors, we have all been there!
Develop the ability to use this method as you walk, it is a great way of
checking your navigation on the fly.
Be aware, this is northern hemisphere specific, it is possible to do in the southern hemisphere but the technique is completely different.

Hasty Method
As good as the Instant Method is it has a couple of failings, if you
cannot see the sun for clouds or mist it is unusable, it relies on a
humans accuracy in pointing the watch in the correct direction, and
without knowledge of the correct time you are stuck!
This second method overcomes all those potential pitfalls but it has a
couple of its own; it is only slightly more accurate than the first method
and it needs 20 minutes or so to complete. Its big plus point is that it
works so long as the sun is strong enough to create a shadow.
• Place a straight stick vertically in the ground and mark clearly
where the end of the shadow is cast.
• After a period of time, the longer the better, place a second stone where the shadow now falls.
• The line between the two stones is the West-East line.
Don’t make the relatively common mistake of transposing the two and getting things horribly wrong. Just remember the sun travels from East to West so the shadow moves West to East!

Deliberate Method
The third and most accurate method. Key for this last method of determining direction to work is that it is started before midday and ended after. The longer before and after you take the measurements the more accurate you can be.

•Before noon place a stick in the ground in a similar way as for the
previous method.
•Mark the point where the shadow cast by the sun ends with a
•Using a piece of string as a guide scribe an arc around the stick
creating a circle where the first stone rests on the circumference.
•Watch while the shadow shortens, moves east and then lengthens
•Mark the point where the shadow again intersects the arc with a
second stone.
•The line between the two stones is the West-East line.

Important Considerations
All times mentioned in this article are Solar Time, you may need to make adjustments for Daylight Savings Time and similar.
Unfortunately the sun, or more accurately the Earth, does not behave as we wish it might because it tilts on its axis so is not constantly over the equator. If you are in, or near, the tropics (defined as areas of the Earth where the sun is directly overhead at some point in the year) it may be impossible to determine North or South using the instant method. Keep in mind that the two solstices are when the sun is furthest from the equator and the two equinoxes are when it is directly over it.

The Arctic and Antarctic circles are the two areas where the sun refuses to set at midsummer and does not rise in midwinter. There is very little hope of judging the rise and fall enough to navigate by, it gets worse - because the sun is visible at night you will make a 180 degree error if you try these methods when it ‘should’ be dark!
Please practice these methods before you use them, trying to remember if the stones mark East - West or West - East as the smoke is still rising from your vehicle would not be a comfortable situation to find yourself in.

Mark Bradshaw writes of himself:-Born in Manchester, I joined the army at 16 after rebelling against an education that was better than I deserved. I served as a tank gunner before moving into reconnaissance where I became a section commander. I completed soviet studies at the intelligence school at Ashford in Kent then did a stint at the International Long Range Reconnaissance School in Weingarten. I also qualified as a Schools Instructor at the Royal Armoured Corps radio school in Bovington. In my spare time I climbed throughout Germany and Sardinia, and canoed from Guatemala to the Mexican Gulf through Belize. I also managed to spend several winters cross country skiing in Norway. I currently work for a UK Police force in the training department.
Some rights reserved Mark Bradshaw/Mountainboy 2007
tags - navigation sun, orientation, orienteering, direction, finding, compass, bearing, sun navigation, learning navigation, teach yourself navigation, homestudy, online

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